Are the gloves off for motor control?

Developments in MCU performance are creating new opportunities for three-phase motor control solutions, which could lead to greater efficiency in everyday white goods. Which approach is best, hardware of software?

Industrial automation is synonymous with motion control, which in turn conjures up images of sophisticated motor control circuits and it is a market that continues to grow.

According to the latest statistics from IMS Research, a supplier of market research and consultancy services on a range of global electronics markets, the low voltage motor drives market is expected to continue to see growth even during the economic downturn.

The worldwide market for low voltage ac and dc motor drives experienced 'unprecedented' growth in 2007, increasing by 19.7 percent over 2006. Data reported by leading drives suppliers indicate all regions and industry segments exhibited strong growth during the year.

IMS Research stated that the market is expected to continue performing well, despite the global economic downturn, with positive growth forecast for both 2008 and '09, when annual revenue growth should bottom out at 3.7 percent.

The company attributes part of the expected demand to the continued hikes in energy prices, as well as the increased focus on energy efficiency, which will maintain positive revenue growth. It expects an increase of around 10.4 percent throughout the forecast period, to reach an estimated value of $13.6billion by 2012.

Lead by infrastructure expansion in China and India, the Asia Pacific motor drives market experienced the largest amount of growth in 2007; the second largest regional market after EMEA and valued at nearly $2.4billion. The drives market in Asia Pacific is expected to continue growing at the fastest rate over the next five years. However, difficult economic conditions around the globe will slow growth across all regions, with most impact felt in the drives markets in the Americas and Japan. The research company believes that the success of recently introduced government stimulus packages will determine the severity of the market downturn.

According to IMS Research analyst, Jenalea Howell: "Growth of critical industry sectors, government legislation and stimulus packages will provide abundant opportunities for the low voltage motor drives market to come through the recession with positive growth."

The application area for motors is defined in part by their size; the increasing demand for low power motors, operating at or below 1kW, is typified by their use in White Goods. An overall increase in demand for motors also creates an opportunity to introduce new technologies and in this application area, increased demand for efficiency has been coupled with developments in microcontroller technology, that is generating improved solutions that before had been unviable for the domestic market.

An example of this is the use of vector control for motor control, particularly with sensorless feedback. The implementation of vector control typically requires feedback of the current being drawn by the motor's windings, in order to determine the position of the motor. With developments in processing power, vector control can be combined with sensorless feedback to both lower the overall cost of implementation and improve efficiency.

Implementing vector control involves complex mathematics, a task that requires considerable processing power. Interestingly, two leading companies, using the same embedded ARM core, now have products that provide the end user with a choice of implementing vector control in either software or hardware.

The choice to use three-phase vector control may be based on a number of benefits: it offers greater efficiency when driving brushless dc motors or induction motors; it allows for smaller motors to be used for a given power requirement, and in general the motor in question operates more quietly, an important consideration for appliances such as dishwashers, washing machines or air conditioning units. However, it is only with the advent of more affordable processing power that its use has seen increased adoption in these low power application areas.

STMicroelectronics has been targeting this area with its STM32 for over a year now. It integrates an ARM Cortex M3 with the necessary PWM and ADC peripherals to provide a motor control solution that can offer vector control. Stello Matteo Bille is the motor control applications team leader for STMicroelectronics, he explained why vector control is attractive to OEMs: "Previous families of motor controllers were based on 6-step control, where the current waveform is not sinusoidal, but trapezoidal. Vector control offers the possibility to move from this kind of control, where the current is trapezoidal, to a form of control where the current is sinusoidal. In the final application, this means less acoustic noise."